JavaScript Object.propertyIsEnumerable()

let arr = [1, 2, 3, 4];

// check whether the element at
// index 0 is enumerable or not
console.log(arr.propertyIsEnumerable(0));

// Output: true

// check whether length is enumerable or not
console.log(arr.propertyIsEnumerable(arr.length));

// Output: false 

propertyIsEnumerable() Syntax

The syntax of the propertyIsEnumerable() method is:

obj.propertyIsEnumerable(prop)

Here, obj is the object whose property (prop) needs to be checked for enumerability.

propertyIsEnumerable() Parameters

The propertyIsEnumerable() method takes in:

• prop - the name of the property to test

propertyIsEnumerable() Return Value

The propertyIsEnumerable() method returns:

• true - if the property is enumerable and exists in the object
• false - if the property is either not enumerable or if it doesn't exist in the object

Note: Every object has a propertyIsEnumerable() method. This method can determine whether the specified property in an object can be enumerated by a for...in loop.

Example 1: JavaScript Object.propertyIsEnumerable()

// create a simple object
let obj = {
  message: "Hello World!",
};

// check if prop is enumerable
console.log(obj.propertyIsEnumerable("message"));

// Output: true

// check a property that does not exist in the object
console.log(obj.propertyIsEnumerable("random"));

// Output: false

In the above example, the propertyIsEnumerable() method returns true as an output as a message exists in the object obj and is enumerable.

However, we get false as an output while checking whether the non-existent property random is enumerable or not.

Example 2: propertyIsEnumerable() With Built-in Objects

console.log(Math.propertyIsEnumerable("random"));
// Output: false

console.log(Math.propertyIsEnumerable("E")); 

// Output: false

In the above example, the propertyIsEnumerable() method returns false as output while checking whether random and E are enumerable or not.

Here, random and E are two properties of the built-in Math object in JavaScript.

Note: User-created properties are often enumerable (unless explicitly set to false), while most built-in properties are non-enumerable by default.

Recommended Reading:

• JavaScript Object.getPrototypeOf()